In a case of a gasket for sealing a space between surfaces of two members static with respect to each other, it is common practice to form a groove in one of the two members to mount the gasket in the groove in order to prevent displacement of the gasket.
In some cases, on the other hand, because of dimensions or a quality problem caused in molding, it is difficult to form the groove for mounting the gasket in a portion where the gasket is to be mounted. In such cases, it is necessary to employ some structure for positioning the gasket.
In some cases, a portion where a groove for mounting the gasket can be formed and a portion where a groove for mounting the gasket cannot be formed are connected. In such cases, it is conceivable to separately provide a special gasket for the portion where the groove is formed and a special gasket for the portion where the groove is not formed.
However, if the respective gaskets are provided separately, it might be difficult to reliably seal junctions between the portions. Moreover, if the respective gaskets are provided separately, the number of parts increases and the number of operation steps for mounting the gasket increases as well.
Therefore, a gasket that can seal both the portion where the groove is formed and the portion where the groove is not formed is demanded. However, there is no known gasket that can appropriately seal both the portions when the portion where the groove for mounting the gasket is formed and the portion where the groove for mounting the gasket is not formed are connected.
Here, a description will be made of a specific example of a structure that can be adopted, that is, the structure in which the portion where the groove for mounting the gasket can be formed and the portion where the groove for mounting the gasket cannot be formed are connected to each other.
A gasket to be mounted between a cylinder head and a cylinder head cover of an engine of an automobile is mounted in a groove provided to the cylinder head cover, for example.
Because of a structure of the engine, various pipe portions and various connecting holes are provided in a space from an inside of the cylinder head to an inside of the cylinder head cover. As examples of the former, there are a pipe portion forming a flow path for blow-by gas, pipe portions forming flow paths for intaking and exhausting air, and intake and exhaust manifolds. As examples of the latter, there are a spark plug hole and bolt insertion holes.
Therefore, the gasket sometimes needs to be provided to a portion of the pipe portion or the connecting hole where the cylinder head and the cylinder head cover are joined to each other.
For a reason of layout, the pipe portion or the connecting hole may be provided to be adjacent to outer wall portions of the cylinder head and the cylinder head cover in some cases. It is difficult or not preferable to form a groove for mounting a gasket in a wall (partition) forming the pipe portion or the connecting hole in some cases. This is for a reason of space-saving layout or a molding quality reason in producing the cylinder head cover by resin molding.
In such cases, it is conceivable to employ the structure in which the portion (portion of the outer wall) where the groove for mounting the gasket can be formed and the portion (portion of the wall forming the pipe portion or the connecting hole) where the groove for mounting the gasket cannot be formed are connected to each other.
If this structure is employed, from a viewpoint of mounting workability or the like, a gasket that can seal both the portions (a gasket for sealing the portion where it is mounted in the groove and a gasket for sealing the portion where it is not mounted in the groove integrated into one gasket) is demanded. However, it is especially difficult to reliably seal the junction between both the portions and therefore there is no known gasket for appropriately sealing both the portions.
As examples of a structure to which the structure, in which the portion where the groove for mounting the gasket can be formed and the portion where the groove for mounting the gasket cannot be formed are connected to each other, can be applied, there are structures disclosed in Patent Documents 1 to 5.    Patent Document 1: Japanese Patent Application Laid-Open No. 11-223118    Patent Document 2: Japanese Patent Application Laid-Open No. 2006-29364    Patent Document 3: Japanese Patent Application Laid-Open No. 2004-138196    Patent Document 4: Japanese Utility Model No. 2548725    Patent Document 5: Japanese Patent Application Laid-Open No. 2002-61539